Known in the art is a method of automatic control of a chamber filter press (cf., for example, the USSR Inventor's Certificate No. 442 812, Class B 01 D 37/04, J 05 D 27/00, published in 1974). The automatic controlling device realizing the known method is provided with a unit for determination of the termination of the suspension dehydration process when the filter cake reaches a specific water content which is continuously monitored by means of a sensor extending through the rubber membrane and located inside a top control chamber of the horizontal chamber filter press. This sensor is connected to an amplifying device connected to an actuating device of the filter press. The amplifying device is equipped with a sensor in order to set a specific water content level of the filter cake and is provided with a scale for visual control. Continuous monitoring of the water content level of the filter cake, which is the function of the electrical conductivity of the liquid phase in the filter cake, is effected by means of the sensor located in the chamber of the filter press and the amplifying device. The water content of the filter cake is shown on the scale of the amplifier sensor, calibrated to read the percentage ratio of the liquid and solid phases.
When a specific water content of the filter cake is obtained, the amplifier sensor generates a signal to indicate termination of the filtering process, which is delivered, after amplification, to the actuating device of the filter press.
A gland seal in the membrane is to be provided to install the sensor in the filter press chamber. If the membrane is made movable along the sensor, the chamber cannot be hermetically sealed.
The known device is deficient in that the sensor is installed in the upper chamber on the filter press whose chambers are arranged horizontally. The water content of the cake in the upper chamber can substantially differ from that of other chambers and cannot, therefore, be accurately controlled. Moreover, the conductivity of the liquid phase of the filter cake varies with the amount of coagulating agents and soluble salts used, also affecting the accuracy of the water content determination.
To summarize, the known device cannot be used for accurate determination of the average water content of the filter cake in all chambers of the filter press. It is certainly not applicable to filter presses having a vertical arrangement of chambers.
Also known in the art is a device for automatic control of the cake water content in a horizontal chamber filter press (cf., for example, the USSR Inventor's Certificate No. 683 784, Cl. B 01 D 37/04, B 01 D 25/12, published in 1979), which comprises a unit for monitoring the water content of the filter cake in the chambers of the filter press, a measuring vessel for filterate collection, a pipe connecting one of the chambers to the measuring vessel, a filtrate level detector comprising an electrode vertically movable by a hand drive, a scale calibrated in percent of the initial water content, and a locking valve equipped with an electromagnetic drive, and an amplifying-converting unit. The amplifier-converter comprises a step-down transformer, a resistor, a rectifier built around diodes, a semiconductor amplifier, and sound and light indicators.
For effective use of the known device, the content of the solid phase in the suspension has to be determined. It is done in a laboratory and the process takes more time than the actual dehydration of the suspension. Moreover, the water content of the cake is monitored in one chamber only, where it can substantially differ from the average water content of the cake in other chambers of the filter press. The efficiency of the filter press is therefore seriously affected.
Also known in the art is a method for controlling a chamber filter press (cf., for example, the USSR Inventor's Certificate No. 841 650, Cl. B 01 D 37/04, published in 1981) which can be used to control the water content of the filter cake by way of the feed rate and density of the suspension delivered to the filter press. The device realizing the known method comprises a delivery pipeline on which a suspension density transmitter is mounted together with a flowmeter and an actuating device (valve). The device also comprises a comparison unit, a multiplier, an averaging unit, an integrator, a functional unit, an indication unit, and a computing unit.
The output of the suspension density transmitter is connected to one of the inputs of the multiplication unit and an input of the functional unit via the averaging unit. The output of the flowmeter is connected to a second input of the multiplication unit via the integrating unit. The output of the functional unit is connected to a first input of the computing unit, while the output of the multiplication unit is connected to a second input of the computing unit. The first input of the comparison unit is connected to the output of the transmitter, while the second input of the comparison unit is connected to the output of the computing unit. The output of the comparison unit is connected to an input of the indicating device and to the input of the actuating device.
The known device is deficient in that the flow rate of the suspension and its density cannot be determined when the content of the solid phase is too high. The termination of the suspension dehydration process is therefore impossible to control with acceptable accuracy.
Also known in the art is a method for automatic control of pressure filters (cf., for example, the USSR Inventor's Certificate No. 680 749, Cl. B 01 D 37/04, published in 1979). The device realizing this method comprises a unit for determination of the suspension dehydration process length, which is connected to at least one filter press and is equipped with sensor capable of determining, in the process of dehydration, the moment the solid phase reaches specific parameters. The unit also comprises a timer indicating the length of the suspension dehydration process, which is connected (electrically) to the sensor, a control console of pressure filters, whose control outputs are connected to actuating devices of the pressure filters, while the inputs thereof are conencted to an output of a computer memory unit connected to a computer and to the timer.
The control unit is a standard cell through which a specific amount of suspension and filtrate passes within a specific time. The timer supplies the duration of the period in which the specific amount of filtrate passes through the standard cell. This time is fed to the computer and converted to filtration constants which are entered to the computer memory. The operator then uses conversion tables to find, on the basis of the filtration constants, the length of the dehydration process and enters this information to the control consoles of the pressure filters.
This device realizing the known method is deficient in that it relies on the conversion tables to find the length of the suspension dehydration process, the procedure being unreliable and inaccurate.